Circuit device, oscillator, electronic apparatus, and vehicle

ABSTRACT

A circuit device includes a phase comparator that performs phase comparison between an input signal based on an oscillation signal and a reference signal, a processor that performs a digital signal process on phase comparison result data which is a result of the phase comparison so as to generate frequency control data, and an oscillation signal generation circuit that generates the oscillation signal having an oscillation frequency which is set on the basis of the frequency control data. The processor performs the digital signal process by using data used when a hold-over state is ended in a case where the hold-over state occurs due to the absence or the abnormality of the reference signal, and then the hold-over state is ended.

CROSS REFERENCE

This application claims priority to Japanese Patent Application No. 2016-086656, filed Apr. 25, 2016, the entire contents of which are expressly incorporated herein by reference.

BACKGROUND 1. Technical Field

The present invention relates to a circuit device, an oscillator, an electronic apparatus, and a vehicle.

2. Related Art

In the related art, there is an oscillator such as an oven controlled crystal oscillator (OCXO) or a temperature compensated crystal oscillator (TCXO). For example, in a base station, a network router, a measurement apparatus, and the like using such an oscillator as a reference signal source, a phase locked loop (PLL) circuit including the oscillator is configured, and an oscillation signal of the oscillator is synchronized with a reference signal such as a GPS signal. In a case where a reference signal is absent or the reference signal is abnormal, a PLL circuit cannot synchronize an oscillation signal with the reference signal. This state is referred to as a hold-over state.

Regarding a technique of controlling an oscillator in a hold-over state, there is a technique disclosed in, for example, JP-A-2015-115933. In JP-A-2015-115933, a control voltage for a voltage controlled oscillator is generated on the basis of phase difference information of a reference signal and a frame clock signal during a normal operation, and history data of the control voltage is stored in a memory. The history data is sequentially read in a time series from the memory during hold-over, and the control voltage is generated on the basis of the history data.

In a case where a hold-over state occurs, and then the hold-over state is ended, it takes time for a PLL circuit to converge on a lock state. For example, in a case where a phase comparator performs a signal process on a detected phase error so as to generate frequency control data, a signal process may be resumed from an initial state or the like when a hold-over state is ended. In this case, since the signal process is resumed from an initial state or the like, for example, the same time as the time required for the PLL circuit to converge on a lock state at the time of starting of the PLL circuit may be required.

SUMMARY

An advantage of some aspects of the invention is to provide a circuit device, an oscillator, an electronic apparatus, a vehicle, and the like, capable of reducing the time required for a PLL circuit to converge on a lock state when a hold-over state is ended.

The invention can be implemented as the following forms or embodiments.

An aspect of the invention relates to a circuit device including a phase comparator that performs phase comparison between an input signal based on an oscillation signal and a reference signal; a processor that performs a digital signal process on phase comparison result data which is a result of the phase comparison; and an oscillation signal generation circuit that generates the oscillation signal having an oscillation frequency which is set on the basis of frequency control data having undergone the digital signal process, in which the processor performs the digital signal process by using data used when a hold-over state is ended (hold-over end use data) in a case where the hold-over state occurs due to the absence or the abnormality of the reference signal, and then the hold-over state is ended.

According to the aspect of the invention, in a case where the hold-over state is ended, the digital signal process is performed by using the hold-over end use data, and thus it is possible to perform the digital signal process by using the hold-over end use data closer to data in a lock state than initial value data. Consequently, it is possible to reduce time required for a PLL circuit to converge on a lock state compared with a case of performing the digital signal process by using the initial value data when a hold-over state is ended.

In the aspect of the invention, the hold-over end use data may be calculation result data in the digital signal process, held when the hold-over state occurs, or data obtained through a correction process in a hold-over period.

The calculation result data in the digital signal process, held when the hold-over state occurs is, for example, calculation result data in the digital signal process in a lock state before the hold-over state occurs. The data obtained through a correction process in a hold-over period is, for example, data obtained by correcting changes in calculation result data due to various factors. The digital signal process is resumed by using such data when the hold-over state is ended, and thus it is possible to reduce time to reach a lock state.

In the aspect of the invention, the hold-over end use data may be the calculation result data, and the processor may hold the calculation result data in the digital signal process when the hold-over state occurs, and perform the digital signal process by using the held calculation result data in a case where the hold-over state is ended.

With this configuration, calculation of the digital signal process can be temporarily stopped when hold-over state occurs, and the digital signal process can be resumed from the state when the hold-over state is ended. Consequently, the digital signal process can be resumed from the calculation result data closer to a lock state.

In the aspect of the invention, the hold-over end use data may be the data obtained through the correction process, and the correction process may be at least one of an aging correction process and a temperature compensation process.

The aging correction process is a process of correcting a change over time in the oscillation frequency during hold-over so that the oscillation frequency becomes constant. The temperature compensation process is a process of correcting a change in an oscillation frequency due to a change in the environmental temperature so that the oscillation frequency becomes constant. In other words, a digital signal process is resumed when a hold-over state is ended by using such data obtained through the correction process in a hold-over period, and thus it is possible to reduce time to reach a lock state.

In the aspect of the invention, the digital signal process may be a digital filter process, the digital filter process may include a proportion process on the phase comparison result data and an integration process on the phase comparison result data, and, when the hold-over state occurs, result data in the integration process may be held as the hold-over end use data.

A certain extent of time is required for result data to converge on result data in a lock state by starting an integration process from an initial value state and integrating phase comparison result data. In relation to this fact, according to the aspect of the invention, since result data in an integration process included in the digital filter process is held when a hold-over state occurs, the integration process is started from result data in a substantially lock state when a hold-over state is ended, and thus it is possible to reduce time to reach a lock state.

In the aspect of the invention, the processor may stop the digital signal process in a case where the hold-over state occurs, and resume the stopped digital signal process in a case where the hold-over state is ended.

The digital signal process is stopped in a case where the hold-over state occurs, and thus calculation result data in the digital signal process is not updated. Consequently, calculation result data obtained when the hold-over state occurs is held. In the above-described way, calculation result data in the digital signal process when the hold-over state occurs is held, and thus the digital signal process can be resumed by using the held calculation result data in a case where the hold-over state is ended.

In the aspect of the invention, the processor may perform, as the digital signal process, a digital filter process on the phase comparison result data, and may also perform at least one of a temperature compensation process and an aging correction process on the frequency control data, and a process of correcting capacitance characteristics of a variable capacitance capacitor connected to a resonator for generating the oscillation signal.

As mentioned above, the processor performs the digital filter process on the phase comparison result data, and can thus generate the frequency control data on the basis of data obtained after the digital filter process is performed. The processor performs the temperature compensation process, the aging correction process, and the capacitance characteristic correction process along with the digital filter process. For example, a plurality of processes can be performed by sharing hardware such as a DSP. Consequently, a circuit scale of the processor can be reduced compared with a case where each process is performed by individual hardware.

In the aspect of the invention, the processor may perform a process of estimating a true value for an observed value of the frequency control data based on the phase comparison result data through a Karman filter process in a period before the hold-over state is detected, and hold a true value at a timing corresponding to a detection timing of the hold-over state in a case where the hold-over state is detected, and perform a calculation process based on the true value so as to generate the frequency control data having undergone aging correction.

According to the aspect of the invention, it is possible to realize aging correction on the basis of a true value which is estimated through the Karman filter process and is held at a timing corresponding to a detection timing of a hold-over state. Therefore, it is possible to realize highly accurate aging correction which cannot be realized in the related art.

Another aspect of the invention relates to an oscillator including any one of the circuit devices; and a resonator that is used to generate the oscillation signal.

Another aspect of the invention relates to an electronic apparatus including any one of the circuit devices.

Another aspect of the invention relates to a vehicle including any one of the circuit devices.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described with reference to the accompanying drawings, wherein like numbers reference like elements.

FIG. 1 is a diagram illustrating a configuration example of a circuit device according to an embodiment.

FIG. 2 is a timing chart for explaining an operation of a phase comparator.

FIG. 3 is a diagram illustrating a relationship between measurement time and a time resolution.

FIG. 4 is a diagram illustrating a first detailed configuration example of the circuit device, a detailed configuration example of the phase comparator, and a first detailed configuration example of a processor according to the embodiment.

FIG. 5 is a diagram illustrating a second detailed configuration example of the circuit device and a detailed configuration example of a loop filter according to the embodiment.

FIG. 6 is a diagram for explaining Modification Example 1 of data used when a hold-over state is ended.

FIG. 7 is a diagram for explaining Modification Example 2 of data used when a hold-over state is ended.

FIG. 8 is a diagram illustrating a modified configuration example of a counter.

FIG. 9 is a third detailed configuration example of the circuit device according to the embodiment.

FIG. 10 is a second detailed configuration example of the processor.

FIG. 11 is a flowchart illustrating a process performed by the processor.

FIG. 12 is a flowchart illustrating details of a low-pass filter process for detecting temperature.

FIG. 13 is a flowchart illustrating details of a Karman filter process and an aging correction process.

FIG. 14 is a flowchart illustrating details of a process in an external PLL mode.

FIG. 15 is a flowchart illustrating details of a process in an internal PLL mode.

FIG. 16 is a diagram illustrating a third detailed configuration example of the processor.

FIG. 17 is a diagram illustrating an example of a measurement result of a variation in an oscillation frequency due to aging.

FIG. 18 is a diagram illustrating a detailed configuration example of an aging corrector.

FIG. 19 is a diagram illustrating a configuration example of an oscillation circuit.

FIG. 20 is a diagram illustrating a configuration example of a circuit device according to a modification example of the embodiment.

FIG. 21 illustrates a circuit configuration example in a case of a direct digital synthesizer method.

FIG. 22 is a diagram illustrating a configuration example of an oscillator including the circuit device according to the embodiment.

FIG. 23 is a diagram illustrating a configuration example of an electronic apparatus including the circuit device according to the embodiment.

FIG. 24 is a diagram illustrating an example of a vehicle including the circuit device according to the embodiment.

FIG. 25 is a diagram illustrating a configuration example of a base station which is one of the electronic apparatuses.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

Hereinafter, a preferred embodiment of the invention will be described in detail. The present embodiment described below is not intended to improperly limit the content of the invention disclosed in the appended claims, and all constituent elements described in the present embodiment are not essential as solving means of the invention.

1. Configuration

FIG. 1 is a diagram illustrating a configuration example of a circuit device 500 according to the present embodiment. The circuit device 500 includes a phase comparator 40 (phase comparison circuit), a processor 50 (processing circuit), and an oscillation signal generation circuit 140.

The phase comparator 40 compares a phase of an oscillation signal OSCK generated by the oscillation signal generation circuit 140 with a phase of a reference signal RFCK, and outputs a result thereof as phase error data PED. Specifically, the phase comparator 40 includes a counter 42 which counts the number of clocks of the oscillation signal OSCK, and outputs the phase error data PED on the basis of a count value in the counter 42. Here, the reference signal RFCK is a pulse signal which is input at a predetermined timing or at a predetermined interval, and is, for example, a signal used as a reference of time. For example, the reference signal RFCK is a reference signal (time pulse) output from a GPS receiver or a reference signal (clock signal) output from a physical layer circuit in a network.

FIG. 2 is a timing chart for explaining an operation of the phase comparator 40. As illustrated in FIG. 2, a cycle of the reference signal RFCK is indicated by Tref. For example, Tref is 1 second in a GPS reference signal. The counter 42 resets a count value thereof at, for example, a rising edge of the reference signal RFCK, and counts the number of clocks of the oscillation signal OSCK for a measurement time Tmes (measurement period) from the edge. The measurement time Tmes is a cycle for performing phase comparison, and corresponds to n cycles of the reference signal RFCK. In other words, phase errors accumulated for the measurement time Tmes are detected. As will be described later, n is an integer which can be set to 2 or more. In a case where a count value when the measurement time Tmes is finished is indicated by NB, a difference (n×FCW-NB) between an expected value n×FCW and the count value NB is output as the phase error data PED. FCW indicates frequency setting data for setting a frequency of the oscillation signal OSCK.

Here, an exemplary case where the counter 42 is counted up from an initial value of “0” has been described, but any other configuration may be used. For example, as will be described later, there may be a configuration in which countdown is performed with the expected value n×FCW as an initial value, and a count value when the measurement time Tmes is finished becomes (n×FCW-NB).

The processor 50 performs various digital signal processes. Specifically, the processor 50 performs a digital signal process on the phase error data PED from the phase comparator 40, and generates frequency control data DFCQ for controlling a frequency of the oscillation signal OSCK. For example, the processor 50 performs a process of converting the phase error data PED corresponding to a difference between a count value and the expected value n×FCW into phase error data having time as the unit, or a loop filter process (digital filter process) on phase error data. The processor 50 may perform an offset adjustment process (an offset adjustment process between the reference signal RFCK and the oscillation signal OSCK) on phase error data, or various correction processes and the like on frequency control data having undergone the loop filter process. The correction process is, for example, a process (temperature compensation process) of compensating for temperature dependency of an oscillation frequency of a resonator, or a process (capacitance characteristic correction process) of correcting capacitance characteristics of a variable capacitance capacitor (a varicap or the like) for controlling an oscillation frequency. Alternatively, the correction process may be a process (aging correction process) of correcting a change over time in an oscillation frequency in a state in which an oscillator performs self-running oscillation during hold-over. The processor 50 may be implemented by an ASIC circuit such as a gate array, and may be implemented by a processor (for example, a central processing unit (CPU) or a digital signal processor (DSP)) and a program (program module) operating on the processor.

The oscillation signal generation circuit 140 generates the oscillation signal OSCK having an oscillation frequency set on the basis of the frequency control data DFCQ. For example, the oscillation signal generation circuit 140 generates the oscillation signal OSCK having an oscillation frequency which is set on the basis of the frequency control data DFCQ by using the frequency control data DFCQ from the processor 50 and a resonator. As an example, the oscillation signal generation circuit 140 causes the resonator to oscillate with an oscillation frequency set on the basis of the frequency control data DFCQ, so as to generate the oscillation signal OSCK.

The oscillation signal generation circuit 140 may be a circuit which generates the oscillation signal OSCK according to a direct digital synthesizer method. For example, the oscillation signal OSCK having an oscillation frequency set on the basis of the frequency control data DFCQ may be digitally generated by using an oscillation signal from the resonator (an oscillation source with a fixed oscillation frequency) as a reference signal. Alternatively, the oscillation signal generation circuit 140 may be a circuit which generates the oscillation signal OSCK having an oscillation frequency which is set on the basis of the frequency control data DFCQ without using a resonator. For example, the oscillation signal generation circuit 140 may be formed of a D/A conversion circuit which converts the frequency control data DFCQ into a control voltage, or a voltage controlled oscillation circuit (VCO) which oscillates at an oscillation frequency set on the basis of the control voltage. Alternatively, the oscillation signal generation circuit 140 may be formed of a CR oscillation circuit including a variable capacitor whose capacitance is variably controlled according to the frequency control data DFCQ. The CR oscillation circuit oscillates at an oscillation frequency set on the basis of the capacitance of the variable capacitor.

A PLL circuit is formed of the phase comparator 40, the processor 50, the oscillation signal generation circuit 140, and thus the oscillation signal OSCK synchronized with the reference signal RFCK is generated. In other words, the processor 50 performs negative feedback control on the phase error data PED through proportional-integral (PI) control or the like, so as to generate the frequency control data DFCQ in which a phase error is reduced (close to zero). The oscillation signal generation circuit 140 generates the oscillation signal OSCK on the basis of the frequency control data DFCQ, and thus generates the oscillation signal OSCK synchronized with the reference signal RFCK.

Meanwhile, in a case where the reference signal RFCK is absent or abnormal for some reason (for example, when a GPS receiver cannot capture a GPS satellite), the PLL circuit cannot synchronize the oscillation signal OSCK with the reference signal RFCK. In a hold-over state caused by the absence or abnormality of the reference signal RFCK, the phase comparator 40 does not output (update) the phase error data PED, and thus the processor 50 cannot generate the frequency control data DFCQ through a digital signal process on phase comparison result data. In this case, time synchronization may be maintained by generating any frequency control data DFCQ so as to cause self-running oscillation. For example, as will be described later in FIG. 10 or the like, the processor 50 performs an aging correction process so as to generate frequency control data AC(k) in a hold-over period, and outputs the frequency control data DFCQ to the oscillation signal generation circuit 140 on the basis of the frequency control data AC(k).

In a case where the reference signal RFCK is recovered in a self-running state during hold-over, synchronous oscillation in the PLL circuit is resumed from the self-running oscillation since the hold-over state is ended. In other words, the phase comparator 40 outputs (updates) the phase error data PED again, and the processor 50 generates the frequency control data DFCQ through a digital signal process on phase comparison result data. In this case, if the digital signal process on phase comparison result data is resumed from an initial state (for example, a state in which calculation result data (intermediately generated data) in the digital signal process is set to an initial value), it takes time for the PLL circuit to reach a lock state from the end of the hold-over state.

Therefore, in the present embodiment, the circuit device 500 includes the phase comparator 40 which performs phase comparison between an input signal based on the oscillation signal OSCK and the reference signal RFCK; the processor 50 which performs a digital signal process on phase comparison result data which is a result of the phase comparison; and the oscillation signal generation circuit 140 which generates the oscillation signal OSCK having an oscillation frequency which is set on the basis of the frequency control data DFCQ obtained after the digital signal process is performed. In a case where a hold-over state occurs due to the absence or the abnormality of the reference signal RFCK, and then the hold-over state is ended, the processor 50 performs a digital signal process by using data used when the hold-over state is ended (hereinafter, simply referred to as hold-over end use data).

Specifically, the processor 50 includes a hold-over end use data register 120 which stores hold-over end use data. The hold-over end use data is data which is different from initial value data (for example, data in a state in which a register is reset; for example, zero) used for a digital signal process at the time of starting of the PLL circuit (the time when the PLL circuit initially starts a synchronization operation after the circuit device 500 is initialized). As the hold-over end use data, various data for causing a lock state of the PLL circuit to occur earlier than in a case of using initial value data may be employed.

The digital signal process using the hold-over end use data may be various digital signal processes including, for example, a digital filter process, a gain process, and a offset adjustment process. The digital signal process includes, for example, a plurality of steps or feedbacks, and the hold-over end use data is input to data at an intermediate node (a node between the steps, or a node between feedbacks) in the process. This corresponds to performing the digital signal process by using the hold-over end use data.

For example, the hold-over end use data register 120 is a register which temporarily stores calculation result data (intermediately generated data) in the digital signal process in a lock state. In a case where the calculation result data changes within a certain predetermined range, data within the predetermined range or a typical value of the calculation result data is used as the hold-over end use data. Such hold-over end use data is stored in the hold-over end use data register 120 at any timing after a hold-over state occurs until the hold-over state is ended. Alternatively, calculation result data obtained when a hold-over state occurs may be held in the hold-over end use data register 120 as hold-over end use data, and may be used when the hold-over state is ended. Alternatively, data generated through a certain digital signal process which is different from a digital signal process using hold-over end use data may be stored in the hold-over end use data register 120 as hold-over end use data. For example, the digital signal process is a process of estimating data which is appropriate as calculation result data when a hold-over state is ended.

According to the present embodiment, in a case where a hold-over state is ended, a digital signal process is performed by using hold-over end use data, it is possible to reduce time required for the PLL circuit to reach a lock state compared with a case of performing a digital signal process by using initial value data. In other words, when a hold-over state is ended, data used for a digital signal process is hold-over end use data closer to data in a lock state than the initial value data. Consequently, it is possible to reduce time required for data used for a digital signal process to become data in a lock state.

Here, an input signal based on the oscillation signal OSCK is the oscillation signal OSCK as described in FIG. 1, for example. However, the invention is not limited thereto, and an input signal may be a signal obtained by buffering the oscillation signal OSCK, and may be a signal obtained through division of the oscillation signal OSCK. The phase comparison result data is data obtained after the phase comparator 40 performs phase comparison. The phase comparison result data may be data generated in a loop after phase comparison is performed. For example, the phase comparison result data is data obtained by performing predetermined processes (for example, a conversion process, a multiplication process, an addition process, and a filter process) on the phase error data PED output from the phase comparator 40. Alternatively, the phase comparison result data may be the phase error data PED output from the phase comparator 40.

In the present embodiment, the hold-over end use data is calculation result data in a digital signal process, held when a hold-over state occurs, or data obtained through a correction process in a hold-over period.

The calculation result data in a digital signal process, held when a hold-over state occurs is calculation result data in a digital signal process in a lock state. The data obtained through a correction process in a hold-over period is data obtained by correcting changes in calculation result data due to various factors (for example, an environmental factor). A digital signal process is resumed by using such data when a hold-over state is ended, and thus it is possible to reduce time to reach a lock state.

In the present embodiment, hold-over end use data is calculation result data. In this case, the processor 50 holds calculation result data in a digital signal process when a hold-over state occurs, and performs the digital signal process by using the held calculation result data in a case where the hold-over state is ended.

In the above-described way, calculation of a digital signal process can be temporarily stopped when hold-over state occurs, and the digital signal process can be resumed from the state when the hold-over state is ended. The digital signal process can be resumed by using calculation result data which is held at the latest timing as a timing for holding the calculation result data before a hold-over state is ended. Consequently, the digital signal process can be resumed from the calculation result data closer to a lock state.

In the present embodiment, the hold-over end use data is data obtained through a correction process. In this case, the correction process is at least one of an aging correction process and a temperature compensation process.

The aging indicates that an oscillation frequency in self-running oscillation changes over time. The aging correction process is a process of correcting a change over time in the oscillation frequency during hold-over so that the oscillation frequency becomes constant. The temperature compensation process is a process of correcting a change in an oscillation frequency due to a change in the environmental temperature (the temperature of a resonator or the circuit device) so that the oscillation frequency becomes constant. Data obtained through such a correction process may be closer to data in a lock state than in a case where the correction process is not performed. In other words, a digital signal process is resumed when a hold-over state is ended by using such data obtained through the correction process in a hold-over period, and thus it is possible to reduce time to reach a lock state.

In the present embodiment, the digital signal process is a digital filter process. The digital filter process includes a proportion process on phase comparison result data and an integration process on the phase comparison result data. When a hold-over state occurs, result data in the integration process is held as calculation result data.

Specifically, a loop filter 55 which will be described later in FIG. 5 performs the digital filter process. In FIG. 5, a multiplier SG1 performs the proportion process, and a multiplier SG2, an adder SAD1, and a register SRG perform the integration process. The register SRG holding result data (output data RTQ) in the integration process corresponds to the hold-over end use data register 120 in FIG. 1. In other words, result data (output data RTQ) when a hold-over state occurs is held in the register SRG without being changed, and the digital filter process is resumed by using the held result data (output data RTQ) when the hold-over state is ended. The hold-over end use data register 120 may be provided separately from the register SRG, data held in the register SRG may be stored (saved) to the hold-over end use data register 120 when a hold-over state occurs, and the data held in the hold-over end use data register 120 may be stored (restored) in the register SRG when the hold-over state is ended.

A certain extent of time is required for result data to converge on result data in a lock state by starting an integration process from an initial value (for example, zero) state and integrating phase comparison result data. In relation to this fact, according to the present embodiment, since result data in an integration process included in the digital filter process is held when a hold-over state occurs, the integration process is started from result data in a substantially lock state when the hold-over state is ended, and thus it is possible to reduce time to reach a lock state.

In the present embodiment, the processor 50 stops a digital signal process in a case where a hold-over state occurs, and resumes the stopped digital signal process in a case where the hold-over state is ended.

Specifically, in a case where a hold-over state occurs, the phase comparator 40 does not output the phase error data PED. Thus, branching to YES in step S7 of a flow illustrated in FIG. 11 does not occur, and thus a process in an internal PLL mode in step S8 including a digital filter process is not performed. For example, in an example illustrated in FIG. 5, the loop filter 55 does not operate, and thus result data (the output data RTQ from the register SRG) in the integration process is not updated. In the above-described way, calculation result data in the digital signal process when a hold-over state occurs is held.

In the present embodiment, the processor 50 performs, as digital signal processes, a digital filter process on phase comparison result data, and at least one of a temperature compensation process and an aging correction process on frequency control data (frequency control data based on data obtained after the digital filter process is performed), and a process of correcting capacitance characteristics of a variable capacitance capacitor connected to a resonator for generating the oscillation signal OSCK.

As mentioned above, the processor 50 performs the digital filter process on phase comparison result data, and can thus generate frequency control data on the basis of data obtained after the digital filter process is performed. Details of generation of the frequency control data will be described later in FIG. 4 and the like. The processor 50 performs the temperature compensation process, the aging correction process, and the capacitance characteristic correction process in a time division manner along with the digital filter process. For example, a DSP which will be described later in FIG. 16 executes a program in which the content of each process is described, and thus a plurality of processes can be performed by sharing a single item of hardware. Consequently, circuits of the processor 50 can be scaled down compared with a case where each process is performed by individual hardware.

In the present embodiment, the processor 50 performs a process of estimating a true value for an observed value of frequency control data based on phase comparison result data through a Karman filter process in a period before a hold-over state is detected. If the hold-over state is detected, the processor 50 holds a true value at a timing corresponding to a detection timing of the hold-over state, and performs a calculation process based on the true value so as to generate frequency control data having undergone aging correction. Details of the Karman filter process and the aging correction will be described later in FIGS. 17 and 18 and the like.

In the above-described way, a true value of frequency control data is estimated through the Karman filter process in a normal operation period, and aging correction is performed on the basis of a true value held at a timing corresponding to a detection timing of a hold-over state in a hold-over period. Various noise components or environmental change components are included in the frequency control data, but a true value is estimated through a Karman filter process, and aging correction is performed on the basis of the true value. Thus, it is possible to realize highly accurate aging correction which cannot be realized in the related art.

In the present embodiment, the phase comparator 40 includes the counter 42 which performs a count operation by using an input signal based on the oscillation signal OSCK, and performs phase comparison of comparing a count value in the counter 42 in n (where n is an integer which can be set to 2 or more) cycles of the reference signal RFCK with the expected value n×FCW of the count value in an integer.

Here, n being an integer which can be set to 2 or more indicates that n can be set to an integer of 2 or more regardless of n being fixed or variable. In other words, in a case where n is fixed, n is set to any one of integers of 2 or more. In a case where n is set to be variable, n is variably set to any one of a plurality of integers including integers of 2 or more. A plurality of integers which can be set may further include 1. In addition, n may be set in a register circuit (for example, the register circuit 32 illustrated in FIG. 9) from an external device of the circuit device 500, or may be set by the circuit device 500 as will be described later in FIG. 8 or the like. Alternatively, n may be set by using a set value stored in a nonvolatile memory (for example, the register circuit 32 illustrated in FIG. 9), fuses, and the like.

According to the present embodiment, the phase comparator 40 performs phase comparison of comparing a count value in the counter 42 with an expected value in integers, and thus the phase comparator 40 can be formed with a simple configuration. Phase comparison results are expressed in integers, and thus it is possible to simplify a process on a phase error.

However, in a case where a count value and an expected value are compared with each other in integers, a phase error in the decimal accuracy cannot be detected, and thus a time resolution (the minimum phase error which can be detected) of a phase error increases compared with a case where a count value and an expected value are compared with each other in decimals. In relation to this fact, according to the present embodiment, the phase comparator 40 compares a count value in the counter 42 in n cycles of the reference signal RFCK with the expected value n×FCW of the count value in integers. In addition, n can be set to 2 or more. Consequently, the time resolution of a phase error can be reduced.

Specifically, the time resolution Tres of a phase error is expressed by the following Equation (1). Tout indicates a cycle of the oscillation signal OSCK. FIG. 3 is a diagram illustrating a relationship between the measurement time Tmes and the time resolution Tres. FIG. 3 illustrates an example of a case where a cycle Tref of the reference signal RFCK is 1 second, and an oscillation frequency (1/Tout) is 40 MHz.

$\begin{matrix} {{Tres} = {\frac{Tout}{{Tmes}/{Tref}} = \frac{Tout}{n}}} & (1) \end{matrix}$

It can be seen from the above Equation (1) and FIG. 3 that n is set to 2 or more so that the measurement time Tmes is increased, and thus the time resolution Tres is reduced. In other words, in the present embodiment, since n can be set to 2 or more, an oscillation signal can be synchronized with the reference signal RFCK with high accuracy, and thus an oscillation frequency can be made highly accurate.

In the present embodiment, n may be set to k1 (where k1 is an integer of 2 or more) in at least a lock state of the PLL circuit including the phase comparator 40.

As mentioned above, since n is set to an integer of 2 or more in the lock state, the time resolution of a phase error in the lock state is reduced, and thus an oscillation signal which is synchronized with the reference signal RFCK with high accuracy can be generated.

In the present embodiment, n may be set to k2 (where k2 is an integer of 1 or more and below k1) at the time of starting of the PLL circuit. The time of starting of the PLL circuit is the time (a so-called pull-in state) until the oscillation signal OSCK is synchronized with the reference signal RFCK after the PLL circuit starts an operation of synchronizing the oscillation signal OSCK with the reference signal RFCK.

In the present embodiment, n is set to k3 (where k3 is an integer of 1 or more and below k1) in the test mode.

As mentioned above, since n (k2 and k3) less than n=k1 in a lock state is set at the time of starting of the PLL circuit or in the test mode, the measurement time Tmes (that is, a cycle for phase comparison) is reduced, and thus the time until the lock state occurs from starting of a synchronization operation can be reduced. In other words, it is possible to achieve the same effect as in so-called gear shift which will be described later in FIG. 5.

In the present embodiment, n may be set to be variable. For example, as will be described later in FIG. 8, the circuit device 500 may set n to be variable. Alternatively, n may be set to be variable from an external device of the circuit device 500 via the register circuit or the like.

If n is set to be variable, n may be set to a great integer of 2 or more in order to obtain a highly accurate oscillation frequency in a lock state. On the other hand, n may be set to an integer smaller than that in the lock state in order to reduce the pull-in time during starting or the test mode.

2. First Detailed Configuration of Circuit Device

FIG. 4 is a diagram illustrating a first detailed configuration example of the circuit device 500, a detailed configuration example of the phase comparator 40, and a first detailed configuration example of the processor 50 according to the present embodiment. The circuit device 500 includes the phase comparator 40, the processor 50, a dithering processor 160, and the oscillation signal generation circuit 140. The phase comparator 40 includes a synchronization circuit 41 and the counter 42. The processor 50 includes a phase error converter 51, an adder 53, a loop filter 55, a frequency control data converter 57, and a correction processor 59.

The synchronization circuit 41 synchronizes the reference signal RFCK with the oscillation signal OSCK. Specifically, the synchronization circuit 41 is formed of a flip-flop circuit or the like which incorporates the reference signal RFCK by using the oscillation signal OSCK. In other words, the synchronization circuit 41 incorporates a logic level of the reference signal RFCK at an edge of the oscillation signal OSCK with the flip-flop circuit, and outputs a clock signal CKR (or a pulse signal) whose logic level changes in synchronization with the edge of the oscillation signal OSCK.

The counter 42 sets a count value to the expected value n×FCW at a rising edge (or a falling edge) of the clock signal CKR, and counts down the number of clocks of the oscillation signal OSCK from the expected value n×FCW. A count value at a rising edge (or a falling edge) after n cycles of the clock signal CKR is output as the phase error data PED. Here, FCW indicates frequency setting data, and is input from, for example, the register circuit 32 in FIG. 9. For example, the frequency setting data FCW is written to the register circuit 32 from an external device via the digital interface 30. Alternatively, the frequency setting data FCW stored in the storage 34 may be read to the register circuit 32.

The phase error converter 51 converts the phase error data PED which is a difference between a count value in n cycles of the reference signal RFCK and the expected value n×FCW into a time difference corresponding to a phase difference between the reference signal RFCK and the oscillation signal OSCK for one second, and outputs the phase error data QPE as a result of the conversion. Specifically, calculation expressed by the following Equations (2) and (3) is performed. Here, Kpe indicates a conversion coefficient, fref indicates a frequency of the reference signal RFCK, and fout indicates a frequency of the oscillation signal OSCK.

$\begin{matrix} {{QPE} = {{Kpe} \times {PED}}} & (2) \\ {{Kpe} = \frac{fref}{n \times {fout}}} & (3) \end{matrix}$

The adder 53 performs a process of adding the offset adjustment data OFTC to the phase error data QPE, and outputs the phase error data QPEF as a result of the addition process (offset adjustment). The offset adjustment data OFTC is data for offset adjusting a phase difference between the reference signal RFCK and the oscillation signal OSCK. Since negative feedback control is performed so that a phase error after the offset adjustment is performed becomes zero, a phase error corresponding to the offset adjustment data OFTC is added between the reference signal RFCK and the oscillation signal OSCK in a lock state. The offset adjustment data OFTC is input from, for example, the register circuit 32 in FIG. 9. The offset adjustment function may be selected to be enabled or disabled, and, in a case where the offset adjustment function is set to be disabled, the adder 53 outputs the phase error data QPE as the phase error data QPEF.

The loop filter 55 performs a digital filter process on the phase error data QPEF having undergone the offset adjustment, and outputs a result thereof as output data QLF. The digital filter process has, for example, a low-pass characteristic or a band-pass characteristic. For example, the loop filter 55 performs a process in which a proportion process of multiplying the phase error data QPEF by a coefficient is combined with an integration process of integrating the phase error data QPEF. A process performed by the loop filter 55 is not limited thereto, and may be a process of calculating the output data QLF so that the phase error data QPEF is close to zero (that is, the phase error data QPEF converges on the output data QLF when the PLL circuit is locked).

The frequency control data converter 57 converts the output data QLF from the loop filter 55 into frequency control data QDF. Specifically, calculation expressed by the following Equations (4) and (5) is performed. Here, Kdco indicates a conversion coefficient. In addition, 2¹⁶−1 is a range (that is, DITQ is 16-bit data) of values of frequency control data DITQ which is input to the oscillation signal generation circuit 140. Further, fmax indicates an upper limit frequency of a frequency change range of the oscillation signal OSCK, and fmin indicates a lower limit frequency of the frequency change range of the oscillation signal OSCK. For example, a frequency of the oscillation signal OSCK obtained in a case where the frequency control data DITQ having the maximum value 2¹⁶-1 is input to the oscillation signal generation circuit 140 is fmax, and a frequency of the oscillation signal OSCK obtained in a case where the frequency control data DITQ having the minimum value 0 is input to the oscillation signal generation circuit 140 is fmin. The invention is not limited thereto, and, for example, a margin may be provided so that fmax and fmin may be set outside an actual oscillation frequency change range corresponding to a range of values of the frequency control data DITQ. For example, individual variations of resonators or the like may be measured, and fmax and fmin may be set on the basis of measurement results. Here, the frequency control data DITQ is 16 bits, but the frequency control data DITQ is not limited to 16 bits.

$\begin{matrix} {{QDF} = {{Kdco} \times {QLF}}} & (4) \\ {{Kdco} = \frac{\left( {2^{16} - 1} \right) \times {fout}}{{fmax} - {fmin}}} & (5) \end{matrix}$

The correction processor 59 performs various correction processes on the frequency control data QDF so as to output the frequency control data DFCQ having undergone the correction processes. As described above, the correction processes are, for example, the temperature compensation process and the capacitance characteristic correction process. The correction processor 59 may perform the aging correction process during hold-over so as to generate the frequency control data DFCQ.

Each element of the processor 50 may be formed of individual hardware, and may be formed of a program operating on the processor. In a case where each element of the processor 50 is formed of the program, for example, each element of the processor 50 is formed of a program module corresponding thereto. The program may be stored as data in a ROM or the like, and may be implemented in hardware such as a gate array which outputs data corresponding to the program.

The dithering processor 160 performs a dithering process on the frequency control data DFCQ so as to output the frequency control data DITQ having undergone the dithering process. The oscillation signal generation circuit 140 generates the oscillation signal OSCK having an oscillation frequency which is set on the basis of the frequency control data DITQ. For example, the processor 50 performs calculation by using 32-bit floating-point data. The dithering processor 160 converts the frequency control data DFCQ which is 32-bit floating-point data into the frequency control data DITQ which is 16-bit integer data, and performs a dithering process during the conversion. For example, the dithering process is a process of reducing or randomizing a quantization error when rounding off broken numbers.

3. Second Detailed Configuration of Circuit Device

FIG. 5 is a diagram illustrating a second detailed configuration example of the circuit device 500 and a detailed configuration example of the loop filter 55 according to the present embodiment. FIG. 5 does not illustrate the correction processor 59, the dithering processor 160, and the oscillation signal generation circuit 140.

The circuit device 500 includes the phase comparator 40, the processor 50, a lock detector 70 (lock detection circuit), and a selector 75. In FIG. 5, the loop filter 55 includes multipliers SG1 and SG2, adders SAD1 and SAD2, and a register SRG.

The lock detector 70 detects whether or not the PLL circuit is in a lock state on the basis of the phase error data PED, sets a lock detection signal DTL to be inactive (a first logic level; for example, a low level) in a case where the PLL circuit is not in a lock state, and sets the lock detection signal DTL to be active (a second logic level; for example, a high level) in a case where the PLL circuit is in a lock state. For example, the lock detector 70 determines that the PLL circuit is in a lock state in a case where the phase error data PED is within a predetermined range. For example, in a case where the phase error data PED is “0” in a lock state, the PLL circuit is determined as being in a lock state if −1≦PED≦+1. The lock detector 70 is formed of, for example, a logic circuit. The lock detector 70 may be included in the processor 50.

The selector 75 selects a coefficient for a proportion process in the loop filter 55 on the basis of the lock detection signal DTL. Specifically, the selector 75 selects a coefficient GA1 in a case where the lock detection signal DTL is inactive, and selects a coefficient GA2 in a case where the lock detection signal DTL is active. The selector 75 outputs the selected coefficient as a coefficient GA. The coefficient GA2 is expressed in the following Equation (6). The coefficient GA1 is a coefficient satisfying a range shown in the following Expression (7). Here, fc indicates a cutoff frequency of the loop filter 55. The coefficients GA1 and GA2 are input from, for example, the register circuit 32 in FIG. 9.

$\begin{matrix} {{{GA}\; 2} = \frac{2\pi \; {fc}}{fref}} & (6) \\ {{{GA}\; 2} \leq {{GA}\; 1} \leq 1} & (7) \end{matrix}$

The multiplier SG1 of the loop filter 55 multiplies the phase error data QPEF by the coefficient GA for the proportion process so as to output a result thereof as output data GQ1.

The multiplier SG2 multiples the phase error data QPEF by a coefficient GRH for an integration process so as to output a result thereof as output data GQ2. The coefficient GRH is a coefficient satisfying a range shown in the following Expression (8). The coefficient GRH is input from, for example, the register circuit 32 in FIG. 9.

$\begin{matrix} {0 \leq {GRH} \leq \frac{\left( {{GA}\; 2} \right)^{2}}{2}} & (8) \end{matrix}$

The adder SAD1 and the register SRG form an integrator. In other words, the adder SAD1 adds the output data GQ2 to output data RTQ from the register SRG, so as to output a result thereof as output data ADQ. The register SRG holds the output data ADQ, and outputs the held data as the output data RTQ.

The adder SAD2 adds the output data GQ1 which is a result of the proportion process to the output data RTQ which is a result of the integration process, and outputs a result thereof as output data QLF. A transfer function H(z) of the loop filter 55 is as in the following Equation (9).

$\begin{matrix} {{H(z)} = \frac{{{GA}\; 2} + {\left( {{GRH} - {{GA}\; 2}} \right)z^{- 1}}}{1 - z^{- 1}}} & (9) \end{matrix}$

The coefficient GA1 for the proportion process selected in an unlock state is used for a function (hereinafter, referred to as gear shift function) of reducing the time required for the unlock state to converge on a lock state. In other words, as shown in the above Expression (7), in the unlock state, the proportion process is performed by using the coefficient GA1 more than the coefficient GA2 in the lock state. Consequently, an effect (negative feedback for a phase error) of causing a phase error to converge acts more strongly than in a lock state, and the time required to converge on a lock state is reduced more than in a case where the gear shift function is not used.

In FIG. 5, the register SRG corresponds to the hold-over end use data register 120 in FIG. 1. As described above, an example of the hold-over end use data is result data (output data RTQ) in an integration process, and, in this case, data held in the register SRG when a hold-over state occurs is held in the register SRG without being changed. The hold-over end use data is not limited thereto, and may have, for example, the following modification examples.

FIG. 6 is a diagram for explaining Modification Example 1 of the hold-over end use data. In FIG. 6, the loop filter 55 further includes a selector SHD. The multipliers SG1 and SG2, and the adders SAD1 and SAD2 in FIG. 5 are not illustrated.

A signal HOLDOVER is active when a hold-over state occurs. In a case where the signal HOLDOVER is inactive, the selector SHD selects output data ADQ from the adder SAD1, and outputs the selected data to the register SRG. In this case, the integration process described in FIG. 5 is performed. On the other hand, in a case where the signal HOLDOVER is active, the selector SHD selects hold-over end use data HKD from the register circuit 32, and outputs the selected data to the register SRG. The register SRG incorporates the hold-over end use data HKD when the signal HOLDOVER is brought into an active state from an inactive state. Since the signal HOLDOVER is inactive, the selector SHD selects the output data ADQ from the adder SAD1 and integrates the data, but data held in the register SRG at this time is started from the hold-over end use data HKD.

The hold-over end use data HKD may be written to the register circuit 32 from an external device via, for example, the digital interface 30 in FIG. 9. Alternatively, the hold-over end use data HKD may be stored in the storage 34 in FIG. 9 in advance, and the hold-over end use data HKD may be read from the storage 34 to the register circuit 32.

FIG. 7 is a diagram for explaining Modification Example 2 of the hold-over end use data. In FIG. 7, the processor 50 includes a temperature compensator 58 and an aging corrector 56 as the correction processor 59. The processor 50 includes a data generator 60 which generates the hold-over end use data HKD on the basis of result data in a correction process. The loop filter 55 further includes the selector SHD. The multipliers SG1 and SG2, and the adders SAD1 and SAD2 in FIG. 5 are not illustrated.

Operations of the selector SHD and the register SRG are the same as those in FIG. 6, and, thus, hereinafter, amethod of generating hold-over end use data will be described.

First, a description will be made of a case of generating hold-over end use data through a temperature compensation process.

The temperature compensator 58 generates temperature compensation data TCODE on the basis of temperature detection data (DTD in FIG. 9). As will be described later in FIG. 10, temperature-compensated frequency control data QDF′ is obtained by adding the temperature compensation data TCODE to the frequency control data QDF. In this case, the frequency control data QDF is data which does not depend on a temperature change in a lock state of the PLL circuit, and the output data RTQ from the register SRG in FIG. 5 is also data which does not depend on a temperature change. On the other hand, in a case where a temperature compensation process is set to be disabled, the PLL circuit controls frequency control data by also taking into consideration a temperature change of an oscillation frequency, and thus the frequency control data QDF depends on a temperature change. In this case, if a temperature changes during a hold-over period, the output data RTQ from the register SRG when a hold-over state occurs may be different from the output data RTQ from the register SRG when the hold-over state is ended.

In the present embodiment, this change is corrected by using the temperature compensation data TCODE. Specifically, in a case where the temperature compensation process is set to be disabled, the temperature compensator 58 generates the temperature compensation data TCODE twice in a case where the signal HOLDOVER is brought into an active state from an inactive state and a case where the signal HOLDOVER is brought into an inactive state from an active state. The temperature compensation data TCODE generated in the former case is referred to as temperature compensation data TCODE1, and the temperature compensation data TCODE generated in the latter case is referred to as temperature compensation data TCODE2. The register SRG holds the output data RTQ when the signal HOLDOVER is brought into an active state from an inactive state. The data generator 60 generates the hold-over end use data HKD on the basis of the temperature compensation data TCODE1, the temperature compensation data TCODE2, and the output data RTQ. Specifically, an inverse number of the coefficient Kdco in the above Equation (5) is multiplied by (TCODE2−TCODE1), and result data thereof is added to the output data RTQ held when the signal HOLDOVER is brought into an active state from an inactive state. Data obtained through this addition is the hold-over end use data HKD.

Next, a description will be made of a case of generating hold-over end use data through an aging correction process.

The aging corrector 56 outputs frequency control data AC(k) at each time step k in a hold-over period. The frequency control data AC(k) is frequency control data in which a change amount due to aging is corrected. The data generator 60 generates the hold-over end use data HKD on the basis of the frequency control data AC(k) when the signal HOLDOVER is brought into an inactive state from an active state (at the latest time step k). Specifically, an inverse number of the coefficient Kdco in the above Equation (5) is multiplied by the frequency control data AC(k), and result data thereof is used as the hold-over end use data HKD.

In a case where hold-over end use data is generated by using both of the temperature compensation process and the aging correction process, for example, the following process is performed. In other words, the data generator 60 adds the temperature compensation data TCODE2 to the frequency control data AC(k) at the time of the signal HOLDOVER being brought into an inactive state from an active state, multiplies result data thereof by an inverse number of the coefficient Kdco, and uses result data thereof as the hold-over end use data HKD.

4. Modification Example of Counter

FIG. 8 illustrates a modified configuration example of the counter 42. The counter 42 includes a shifter 44, a down counter 45, a phase error register 46, and an error determination circuit 48.

In this modification configuration example, the measurement time Tmes is controlled to be variable, and thus a function equivalent to the gear shift function is realized. In a case of using the modified configuration example, constituent elements (the lock detector 70 and the selector 75) related to the gear shift function in FIG. 5 may be omitted.

The shifter 44 shits bits of the frequency setting data FCW in a shift amount corresponding to a shift amount control signal CSF. Specifically, n in the measurement time Tmes=nxTref can be set to 2j (where j is an integer of 0 or more), and j indicates a shift amount. The shifter 44 shifts the frequency setting data FCW toward the MSB side by j bits, and outputs a result thereof as an expected value SFCW (=n×FCW). The shifter 44 updates the expected value SFCW at a rising edge (or a falling edge) of the clock signal CKR.

The down counter 45 initializes a count value to the expected value SFCW at a rising edge (or a falling edge) of the clock signal CKR. The down counter 45 counts down by using the oscillation signal OSCK up to a rising edge (or a falling edge) of the clock signal CKR for the measurement time Tmes, and outputs a count value QDC thereof.

The phase error register 46 incorporates the count value QDC in the down counter 45 at a rising edge (or a falling edge) of the clock signal CKR at the time of finishing of the measurement time Tmes, and outputs the incorporated count value as the phase error data PED.

The error determination circuit 48 determines whether or not an absolute value of the phase error data PED is equal to or smaller than a threshold value THR, and outputs the shift amount control signal CSF on the basis of a determination result. Specifically, the error determination circuit 48 increases a shift amount (the number of bits j) by 1 in a case where an absolute value of the phase error data PED is equal to or smaller than the threshold value THR. For example, a shift amount is increased by 1, such as j=0, 1, 2, . . . , and jmax. Here, jmax is the maximum value of a shift amount, and is a shift amount in a lock state (that is, n=2jmax in a lock state). An initial value of j may be an integer of 1 or more. In addition, j may be increased by an integer of 2 or more. The threshold value THR is input from, for example, the register circuit 32 in FIG. 9.

The error determination circuit 48 outputs a control signal CKPE for a conversion coefficient Kpe to the phase error converter 51 on the basis of the determination result. Specifically, the conversion coefficient Kpe depends on n as in the above Equation (3). The error determination circuit 48 outputs the control signal CKPE for designating the conversion coefficient Kpe in a case of n=2j in conjunction with the shift amount j. For example, a conversion coefficient corresponding to each value of j may be stored in the register circuit 32 or the like in FIG. 9 in advance, and the phase error converter 51 may select the conversion coefficient Kpe according to the control signal CKPE. Alternatively, a conversion coefficient in a reference shift amount (for example, j=0) may be stored in the register circuit 32 or the like in FIG. 9, and the phase error converter 51 may perform calculation corresponding to the control signal CKPE on the conversion coefficient read from the register circuit 32 or the like so as to obtain the conversion coefficient Kpe.

The error determination circuit 48 outputs a lock detection signal DTL′ on the basis of a determination result of whether or not an absolute value of the phase error data PED at j=jmax is equal to or smaller than the threshold value THR. In other words, in a case where an absolute value of the phase error data PED is equal to or smaller than the threshold value THR, the lock detection signal DTL′ is made active.

5. Third Detailed Configuration of Circuit Device

FIG. 9 is a diagram illustrating a third detailed configuration example of the circuit device 500 according to the present embodiment.

The circuit device 500 includes a temperature sensor 10, an A/D converter 20 (A/D conversion circuit), the digital interface 30 (digital interface circuit), the register circuit 32, the storage 34 (memory), the phase comparator 40, the processor 50, the lock detector 70, a reference signal detection circuit 47, and the oscillation signal generation circuit 140.

The temperature sensor 10 outputs a temperature detection voltage VTD. Specifically, a temperature-dependent voltage which changes depending on the temperature of the environment (circuit device 500) is output as the temperature detection voltage VTD. For example, the temperature sensor 10 may be formed of a diode or a bipolar transistor. A forward voltage of a PN junction included in the diode or the bipolar transistor corresponds to the temperature detection voltage VTD.

The A/D converter 20 performs A/D conversion on the temperature detection voltage VTD from the temperature sensor 10 so as to output temperature detection data DTD. For example, the digital temperature detection data DTD (A/D result data) corresponding to an A/D conversion result of the temperature detection voltage VTD is output. As an A/D conversion method in the A/D converter 20, for example, a successive comparison method or a method similar to the successive comparison method may be employed. An A/D conversion method is not limited to such methods, and various methods (a counting type, a parallel comparison type, and a series/parallel type) may be employed.

A resonator XTAL is provided outside the circuit device 500, and is, for example, an AT cut or SC cut quartz crystal resonator which is of a thickness shear vibration type, or a flexural vibration type piezoelectric resonator. The resonator XTAL may be a resonator (an electromechanical resonator or an electrical resonance circuit). As the resonator XTAL, a surface acoustic wave (SAW) resonator as a piezoelectric resonator, a microelectromechanical system (MEMS) resonator as a silicon resonator, and the like may be used. As a substrate material of the resonator XTAL, a piezoelectric single crystal of quartz crystal, Lithium Tantalate, or Lithium Niobate, a piezoelectric material such as piezoelectric ceramics of lead zirconate titanate or the like, or a silicon semiconductor material may be used. The resonator XTAL may be excited due to a piezoelectric effect, and may be excited by using electrostatic driving based on a Coulomb force.

The oscillation signal generation circuit 140 includes a D/A converter 80 and the oscillation circuit 150. The D/A converter 80 performs D/A conversion on the frequency control data DFCQ from the processor 50. As a D/A conversion type of the D/A converter 80, for example, a resistance string type (resistance division type) may be employed. However, a D/A conversion type is not limited thereto, and various types such as a resistance ladder type (R-2R ladder type or the like), a capacitor array type, and a pulse width modulation type may be employed. The D/A converter 80 may include a control circuit, a modulation circuit (a PWM circuit), a filter circuit, or the like, in addition to a D/A converter. The oscillation circuit 150 generates the oscillation signal OSCK by using an output voltage VQ from the D/A converter 80, and the resonator XTAL. The oscillation circuit 150 causes the resonator XTAL (a piezoelectric resonator, a resonator, or the like) to oscillate so as to generate the oscillation signal OSCK. Specifically, one end of the resonator XTAL is connected to the oscillation circuit 150 via a first resonator terminal TX1 of the circuit device 500, and the other end of the resonator XTAL is connected to the oscillation circuit 150 via a second resonator terminal TX2 of the circuit device 500. The oscillation circuit 150 causes the resonator XTAL to oscillate at an oscillation frequency at which the output voltage VQ of the D/A converter 80 is used as a frequency control voltage (oscillation control voltage). For example, in a case where the oscillation circuit 150 is a circuit (VCO) which controls oscillation of the resonator XTAL through voltage control, the oscillation circuit 150 may include a variable capacitance capacitor (a varicap or the like) whose capacitance value varies depending on a frequency control voltage.

The reference signal detection circuit 47 detects whether or not the reference signal RFCK is absent or abnormal, and outputs a reference signal detection signal SYNCCLK on the basis of a detection result. In a case where it is detected that the reference signal RFCK is present or normal, the detection signal SYNCCLK becomes active (second logic level). In a case where it is detected that the reference signal RFCK is absent or abnormal, the detection signal SYNCCLK becomes inactive (first logic level). For example, the reference signal detection circuit 47 detects whether or not the reference signal RFCK is absent or abnormal by monitoring a pulse (or a frequency) of the reference signal RFCK. For example, a pulse interval of the reference signal RFCK is measured with a counter or the like, and in a case where it is determined that pulses are not input for a predetermined period on the basis of a count value, the reference signal RFCK is determined as being absent or being abnormal. Alternatively, in a case where an input interval of pulses continues in a state of exceeding a predetermined range for a predetermined period on the basis of a count value, the reference signal RFCK is determined as being absent or being abnormal.

The storage 34 stores various pieces of information which is necessary in various processes or operations of the circuit device 500. The storage 34 may be implemented by, for example, a nonvolatile memory. As the nonvolatile memory, for example, an EEPROM may be used. For example, a metal-oxide-nitride-oxide-silicon (MONOS) type memory may be used as the EEPROM. Alternatively, memories of other types such as a floating gate type may be used as the EEPROM. The storage 34 may be implemented by, for example, a fuse circuit as long as information can be held and stored even in a state in which power is not supplied.

The register circuit 32 is a circuit formed of a plurality of registers such as a status register, a command register, and a data register. An external device (for example, a processor such as a CPU or an MPU) of the circuit device 500 accesses each register of the register circuit 32 via the digital interface 30. The external device can check a status of the circuit device 500, issue a command to the circuit device 500, transmit data to the circuit device 500, and read data from the circuit device 500, by using the register of the register circuit 32. The register circuit 32 stores information which is read from the storage 34. For example, parameters such as the above-described conversion coefficients Kpe and Kdco, the offset adjustment data OFTC, and the coefficients GA1, GA2 and GRH are stored in the storage 34. The parameters are read (initially loaded) to the register circuit 32, for example, at the time of starting of the circuit device 500. The processor 50 performs a process using the parameters by referring to the register circuit 32.

The processor 50 includes an internal PLL processor 83, a hold-over processor 52, a Karman filter 54, an aging corrector 56, and a temperature compensator 58. The Karman filter 54, the aging corrector 56, and the temperature compensator 58 correspond to the correction processor 59 in FIG. 4. The internal PLL processor 83 corresponds to the phase error converter 51, the adder 53, the loop filter 55, and the frequency control data converter 57 described in FIG. 4 or the like. Hereinafter, a process performed by the internal PLL processor 83 will be referred to as an internal PLL process. The hold-over processor 52 performs various processes regarding hold-over. The Karman filter 54 performs a process of estimating a true value for an observed value of frequency control data. The aging corrector 56 performs aging correction for compensating for a frequency change due to aging during hold-over. The temperature compensator 58 performs a temperature compensation process on an oscillation frequency on the basis of the temperature detection data DTD from the A/D converter 20.

The digital interface 30 is an interface for inputting and outputting digital data between the circuit device 500 and an external device (for example, a microcomputer or a controller). The digital interface 30 may be implemented on the basis of, for example, a synchronous serial communication method using serial clock lines and serial data lines. Specifically, the digital interface 30 may be implemented on the basis of an inter-integrated circuit (I2C) method or a 3-wire or 4-wire serial peripheral interface (SPI) method. The I2C method is a synchronous serial communication method of performing communication by using two signal lines such as a serial clock line SCL and a bidirectional serial data line SDA. The SPI method is a synchronous serial communication method of performing communication by using a serial clock line SCK and two unidirectional serial data lines SDI and SDO. The digital interface 30 is formed of an input/output buffer circuit, a control circuit, and the like realizing such a communication method.

The reference signal RFCK is input to the circuit device 500 via a connection terminal (pad) of the circuit device 500. A signal PLOCK for performing a notification of whether or not an external PLL circuit is in a lock state is input to the circuit device 500 via the connection terminal (pad) of the circuit device 500. The signal PLOCK may be input to the circuit device 500 via the digital interface 30. For example, the signal PLOCK becomes inactive in a case where the external PLL circuit is not in a lock state, and becomes active in a case where the external PLL circuit is in a lock state.

In the present embodiment, for example, if an external device writes mode setting information to the register circuit 32 via the digital interface 30, one of the internal PLL mode (first mode) and the external PLL mode (second mode) is set.

In the internal PLL mode, the processor 50 performs an internal PLL process on the basis of the phase error data PED from the phase comparator 40, so as to generate frequency control data (QDF in FIG. 4). The processor 50 performs signal processes such as a temperature compensation process on the frequency control data QDF so as to output the frequency control data DFCQ having undergone the signal processes to the oscillation signal generation circuit 140. The oscillation signal generation circuit 140 generates the oscillation signal OSCK by using the frequency control data DFCQ and the resonator XTAL so as to output the oscillation signal OSCK to the phase comparator 40. Consequently, a loop of a PLL circuit (internal PLL circuit) is formed by the phase comparator 40, the oscillation signal generation circuit 140, and the like.

In the external PLL mode, frequency control data DFCE (externally generated frequency control data) from an external frequency control data generator is input to the processor 50 via the digital interface 30. The processor 50 performs signal processes such as a temperature compensation process on the frequency control data DFCE so as to output the frequency control data DFCQ having undergone the signal processes to the oscillation signal generation circuit 140. The oscillation signal generation circuit 140 generates the oscillation signal OSCK by using the frequency control data DFCQ and the resonator XTAL so as to output the oscillation signal OSCK to the external frequency control data generator. Consequently, a loop of a PLL circuit (external PLL circuit) is formed by the external frequency control data generator, the oscillation signal generation circuit 140, and the like.

The external frequency control data generator compares an input signal based on the oscillation signal OSCK with the reference signal RFCK so as to generate the frequency control data DFCE. For example, the external frequency control data generator may include a comparison calculator which performs comparison calculation between the oscillation signal OSCK and the reference signal RFCK, and a digital filter which performs a smoothing process on phase error data. Alternatively, the external frequency control data generator may include a phase comparator of an analog circuit, a filter (loop filter) of an analog circuit, and an A/D converter.

6. Second Detailed Configuration of Processor

FIG. 10 is a second detailed configuration example of the processor 50. The processor 50 includes a centigrade degree converter 81, a low-pass filter 82, the temperature compensator 58, the internal PLL processor 83, the Karman filter 54, the aging corrector 56, a capacitance characteristic corrector 89, adders 84, 85 and 86, and a selector 87. The Karman filter 54, the aging corrector 56, the temperature compensator 58, and the capacitance characteristic corrector 89 correspond to the correction processor 59 in FIG. 4.

The centigrade degree converter 81 converts the temperature detection data DTD into temperature detection data DTD′ indicating a Celsius temperature (in a broad sense, corresponding to a Celsius temperature). For example, the temperature detection data DTD indicating nonlinear characteristics with respect to a Celsius temperature is converted into the temperature detection data DTD′ indicating linear characteristics with respect to a Celsius temperature.

The low-pass filter 82 performs a digital filter process for smoothing a temporal change in the temperature detection data DTD′ so as to output temperature detection data DTD″ having undergone the digital filter process.

The temperature compensator 58 performs a temperature compensation process on the basis of the temperature detection data DTD″, and generates temperature compensation data TCODE (temperature compensation code) for maintaining an oscillation frequency to be constant with respect to a temperature change. Specifically, information regarding coefficients A₀ to A₅ of a polynomial (approximate function) in Equation (10) is stored in the storage 34 in FIG. 9. Here, X corresponds to the temperature detection data DTD″. The temperature compensator 58 reads the information regarding the coefficients A₀ to A₅ from the storage 34, and performs calculation expressed in the following Equation (10) on the basis of the coefficients A₀ to A₅ and the temperature detection data DTD″ (=X) so as to generate the temperature compensation data TCODE.

TCODE=A ₅ ·X ⁵ +A ₄ ·X ⁴ +A ₃ ·X ³ +A ₂ ·X ² +A ₁ ·X+A ₀  (10)

The adder 84 adds the temperature compensation data TCODE to the frequency control data DFCE which is input from the external frequency control data generator in the external PLL mode, and outputs a result thereof as frequency control data DFCE′. The frequency control data DFCE may be output as the frequency control data DFCE′.

The internal PLL processor 83 performs an internal PLL process on the basis of the phase error data PED which is input from the phase comparator 40 in the internal PLL mode, and outputs the frequency control data QDF.

The adder 85 adds the temperature compensation data TCODE to the frequency control data QDF, and outputs a result thereof as frequency control data QDF′. The frequency control data QDF may be output as the frequency control data QDF′.

The Karman filter 54 performs a process of estimating a true value for an observed value of frequency control data (DFCE and QDF) through a Karman filter process in a period (normal operation period) before a hold-over state caused by the absence or abnormality of the reference signal RFCK is detected. This true value is a true value estimated through the Karman filter process, and thus cannot be said to be a real true value. A control process performed due to detection of a hold-over state is performed by the hold-over processor 52 illustrated in FIG. 9. Details of the Karman filter process will be described later.

The aging corrector 56 holds a true value at a timing corresponding to a detection timing of a hold-over state in a case where the hold-over state is detected. A timing at which the true value is held may be a timing at which a hold-over state is detected, and may be a timing prior to the timing. The aging corrector 56 generates frequency control data AC(k) having undergone aging correction by performing a calculation process based on the held true value. Details of the aging correction process will be described later.

The adder 86 adds the temperature compensation data TCODE to the frequency control data AC(k), and outputs a result thereof as frequency control data AC(k)′. The frequency control data AC(k) may be output as the frequency control data AC(k)′.

The selector 87 selects the frequency control data DFCE′ in the external PLL mode during non-hold-over (normal operation), selects the frequency control data QDF′ in the internal PLL mode during non-hold-over, and selects the frequency control data AC(k)′ during hold-over. The selector 87 outputs the selected frequency control data as the frequency control data DFCQ′.

The capacitance characteristic corrector 89 performs a correction process on the frequency control data DFCQ′ so that the frequency control data DFCQ′ uniquely corresponds to an oscillation frequency (the same oscillation frequency is obtained with respect to the same frequency control data DFCQ′), and outputs a result thereof as the frequency control data DFCQ. Specifically, the variable capacitance capacitor (for example, CX1 in FIG. 19) of the oscillation circuit 150 changes the capacitance thereof for a control voltage depending on, for example, an individual variation or a temperature change. The capacitance characteristic corrector 89 performs correction of canceling (reducing) changes in capacitance characteristics. For example, the capacitance characteristic corrector 89 performs a first correction process of canceling (reducing) an individual variation of capacitance characteristics, a second correction process of canceling (reducing) a temperature change of the capacitance characteristics on the basis of the temperature compensation data TCODE, and a third correction process of canceling (reducing) nonlinearity of the capacitance characteristics (capacitance characteristics for the frequency control data DFCQ′ are made linear). The first to third correction processes are performed through calculation of correction expressions corresponding to the respective correction processes. Parameters (coefficients and the like) used for the correction expressions are stored in, for example, the storage 34 in FIG. 9. The parameters are read to the register circuit 32 from the storage 34, and are input to the processor 50 from the register circuit 32. Each of the first to third correction processes may be selected to be enabled and disabled.

7. Process Flow

FIG. 11 is a flowchart illustrating a process performed by the processor 50.

If the process is started, the processor 50 determines whether or not a temperature detection finish flag is active (step S1). The temperature detection finish flag becomes active in a case where the A/D converter 20 outputs (updates) the temperature detection data DTD.

In a case where the temperature detection finish flag is active, the processor 50 performs a low-pass filter process for detecting a temperature (step S2). In other words, the centigrade degree converter 81 converts the temperature detection data DTD into centigrade, and the low-pass filter 82 performs a low-pass filter process on the temperature detection data DTD′. Next, the temperature compensator 58 performs a temperature compensation process on the basis of the temperature detection data DTD″ having undergone the low-pass filter process, and generates the temperature compensation data TCODE (step S3). Next, the Karman filter 54 performs a Karman filter process on the basis of the frequency control data DFCE or QDF. The aging corrector 56 performs an aging correction process during hold-over (step S4). Next, the flow proceeds to step S9.

In a case where the temperature detection finish flag is inactive in step S1, it is determined whether or not a frequency control data write flag is active (step S5). The frequency control data write flag becomes active in a case where the frequency control data DFCE is input (written to the register circuit 32, for example) via the digital interface 30 from the external frequency control data generator.

In a case where the frequency control data write flag is active, the processor 50 performs a process in the external PLL mode (step S6). Specifically, the adder 84 and the selector 87 perform this process. Next, the flow proceeds to step S9.

In a case where the frequency control data write flag is inactive, it is determined whether or not a phase comparison finish flag is active (step S7). The phase comparison finish flag becomes active in a case where the phase comparator 40 outputs (updates) the phase error data PED. Specifically, the phase comparison finish flag becomes active every n cycles of the reference signal RFCK. Alternatively, the phase comparison finish flag may also become active when the phase comparator 40 outputs the phase error data PED for each cycle of the reference signal RFCK. In this case, for example, the same phase error data PED is output for n times, and a value of the phase error data PED changes every n cycles of the reference signal RFCK.

In a case where the phase comparison finish flag is active, the processor 50 performs a process in the internal PLL mode (step S8). Specifically, the internal PLL processor 83, the adder 85, and the selector 87 perform this process. Next, the flow proceeds to step S9.

In a case where the phase comparison finish flag is inactive, the flow returns to step S1, and the loop is repeated until any one of the temperature detection finish flag, the frequency control data write flag, and the phase comparison finish flag becomes active so that flag waiting is performed.

In step S9, the capacitance characteristic corrector 89 performs a capacitance characteristic correction process on the frequency control data DFCQ′ which is a process result in any one of steps S4, S6 and S8, and outputs the frequency control data DFCQ to the oscillation signal generation circuit 140 (or the dithering processor 160) (step S9). Next, the processor 50 resets the flags (step S10). Specifically, among the temperature detection finish flag, the frequency control data write flag, and the phase comparison finish flag, a flag which is active is reset to be inactive. Next, the flow returns to step S1, and flag waiting is performed.

FIG. 12 is a flowchart illustrating details of the low-pass filter process (step S2) for detecting a temperature.

The processor 50 determines whether or not the low-pass filter process is set to be enabled (step S21). In a case where the low-pass filter process is set to be disabled, the process is finished without performing the low-pass filter process. A centigrade conversion process is performed, for example, before step S21.

In a case where the low-pass filter process is set to be enabled, the low-pass filter 82 performs the low-pass filter process on the temperature detection data DTD′ (step S22). Next, it is determined whether or not the cutoff frequency fc in the low-pass filter process is set to fs/4 (step S23). Here, fs indicates an operation frequency of the low-pass filter process. In other words, fs indicates a sampling frequency for the temperature detection data DTD (a frequency at which the A/D converter 20 outputs the temperature detection data DTD).

In a case where the cutoff frequency fc is set to fs/4, the processor 50 determines whether or not the low-pass filter process is performed for four times (whether or not the low-pass filter process is performed on the temperature detection data DTD which is input for four times) (step S24). The process is finished in a case where the low-pass filter process is performed for four times. In a case where the low-pass filter process is not performed for four times, a temperature measurement finish flag is reset to be inactive (step S28), and the flow returns to step S1.

In a case where the cutoff frequency fc is not set to be fs/4, it is determined whether or not the cutoff frequency fc in the low-pass filter process is set to fs/16 (step S25).

In a case where the cutoff frequency fc is set to fs/16, the processor 50 determines whether or not the low-pass filter process is performed for sixteen times (whether or not the low-pass filter process is performed on the temperature detection data DTD which is input for sixteen times) (step S26). The process is finished in a case where the low-pass filter process is performed for sixteen times. In a case where the low-pass filter process is not performed for sixteen times, the temperature measurement finish flag is reset to be inactive (step S28), and the flow returns to step S1.

In a case where the cutoff frequency fc is not set to be fs/16, the cutoff frequency fc is set to fs/64, and thus the processor 50 determines whether or not the low-pass filter process is performed for sixty-four times (whether or not the low-pass filter process is performed on the temperature detection data DTD which is input for sixty-four times) (step S27). The process is finished in a case where the low-pass filter process is performed for sixty-four times. In a case where the low-pass filter process is not performed for sixty-four times, the temperature measurement finish flag is reset to be inactive (step S28), and the flow returns to step S1.

FIG. 13 is a flowchart illustrating details of the Karman filter process and the aging correction process (step S4).

The processor 50 determines whether or not the internal PLL mode is set (step S41). In a case where the internal PLL mode is set, the frequency control data QDF is stored in an input register (AC input) for the Karman filter process (step S42). In a case where the external PLL mode is set (the internal PLL mode is not set), the frequency control data DFCE is stored in the input register for the Karman filter process (step S43).

Next, the processor 50 determines whether or not a hold-over flag (the signal HOLDOVER in FIGS. 6, 7 and 18) is active (step S44). The hold-over flag becomes active in a case where the hold-over processor 52 determines a hold-over state.

In a case where the hold-over flag is inactive, the Karman filter 54 performs the Karman filter process on an input which is selected in step S42 or S43 (step S45). Next, the processor 50 determines whether or not the internal PLL mode is set (step S46). In a case where the internal PLL mode is set, the frequency control data QDF is stored in a register for a variable TReg (step S47). In a case where the external PLL mode is set, the frequency control data DFCE is stored in the register for the variable TReg (step S48).

Next, the processor 50 determines whether or not the temperature compensation process is set to be enabled (step S49). In a case where the temperature compensation process is set to be enabled, a value obtained by adding the variable TReg to the temperature compensation data TCODE is stored in a register for the frequency control data DFCQ′ (step S50). In a case where the temperature compensation process is set to be disabled, the variable TReg is stored in the register for the frequency control data DFCQ′ (step S51). The processes in steps S49 to S51 correspond to processes performed by the adders 84 and 85 and the selector 87.

In a case where the hold-over flag is active in step S44, the aging corrector 56 performs the aging correction process (step S52). Next, the processor 50 determines whether or not the temperature detection finish flag is active (step S53). In a case where the temperature detection finish flag is active, a value obtained by adding the frequency control data AC(k) to the temperature compensation data TCODE is stored in the register for the frequency control data DFCQ′ (step S54). In a case where the temperature detection finish flag is inactive, the frequency control data AC(k) is stored in the register for the frequency control data DFCQ′ (step S55). The processes in steps S53 to S55 correspond to processes performed by the adder 86 and the selector 87.

FIG. 14 is a flowchart illustrating details of the process (step S6) in the external PLL mode.

The processor 50 determines whether or not the temperature compensation process is set to be enabled (step S61). In a case where the temperature compensation process is set to be enabled, a value obtained by adding the frequency control data DFCE to the temperature compensation data TCODE is stored in the register for the frequency control data DFCQ′ (step S62). In a case where the temperature compensation process is set to be disabled, the frequency control data DFCE is stored in the register for the frequency control data DFCQ′ (step S63). The processes in steps S61 to S63 correspond to processes performed by the adder 84 and the selector 87.

FIG. 15 is a flowchart illustrating details of the process (step S8) in the internal PLL mode.

The internal PLL processor 83 performs an internal PLL process on the phase error data PED so as to generate the frequency control data QDF (step S81). Next, the processor 50 determines whether or not the temperature compensation process is set to be enabled (step S82). In a case where the temperature compensation process is set to be enabled, a value obtained by adding the frequency control data QDF to the temperature compensation data TCODE is stored in the register for the frequency control data DFCQ′ (step S83). In a case where the temperature compensation process is set to be disabled, the frequency control data QDF is stored in the register for the frequency control data DFCQ′ (step S84). The processes in steps S82 to S84 correspond to processes performed by the adder 85 and the selector 87.

8. Third Detailed Configuration of Processor

FIG. 16 is a diagram illustrating a third detailed configuration example of the processor 50. FIG. 16 illustrates a configuration example of a case where the processor 50 is formed of a DSP. In other words, the DSP executes commands described in a program, and thus the process described with reference to the functional block diagram of FIG. 10 or the processes described with reference to the flowcharts of FIGS. 11 to 15 are realized.

The processor 50 includes a program counter 91, a program ROM 92, a command decoder 93, a coefficient ROM 94, a register circuit 95, a selector 96, a multiplier 97, a selector 98, an adder 99, and an output register 88.

The program ROM 92 is a read only memory (ROM) storing a program. Program data may be formed by using logic circuits (a combined circuit or the like). For example, the program is formed of a row number, a command corresponding to the row number, and an operand operated according to the command.

The program counter 91 is a counter which outputs a row number of the program. The program ROM 92 outputs a row number, a command, and an operand, designated by a count value in the program counter 91.

The command decoder 93 analyzes the command and the operand, and outputs control signals for the multiplier 97 or the adder 99 performing a process corresponding to the command and the operand. Specifically, the command decoder 93 outputs a multiplier input address for indicating data which is to be input to the multiplier 97, a multiplier input data sign indicating a sign of data which is to be input to the multiplier 97, an adder input address for indicating data which is to be input to the adder 99, an adder input data sign indicating a sign of data which is to be input to the adder 99, and a write address indicating a register address in which data output from the adder 99 is stored.

The coefficient ROM 94 includes a ROM and a selector. Various some coefficients used for calculation performed by the processor 50 are stored in the ROM. Remaining some coefficients are stored in the storage 34, and are read from the storage 34 so as to be stored in the register circuit 32. Coefficients from the ROM and the register circuit 32 and data which is input to the processor 50 are input to the selector. The input data includes, for example, the frequency control data DFCE from the register circuit 32, the phase error data PED from the phase comparator 40, and the temperature detection data DTD from the A/D converter 20. The selector selects a coefficient or input data corresponding to the multiplier input address from the command decoder 93, and outputs the selected coefficient or input data to the selector 96. The selector selects a coefficient or input data corresponding to the adder input address from the command decoder 93, and outputs the selected coefficient or input data to the selector 98.

The register circuit 95 includes a register and a selector. The register temporarily stores data (including intermediately generated data) generated through calculation. For example, the register stores the variable TReg, the temperature compensation data TCODE, and the frequency control data QDF, DFCQ′ and AC(k). The selector selects data corresponding to the multiplier input address from the command decoder 93, and outputs the selected data to the selector 96 or the multiplier 97. The selector selects data corresponding to the adder input address from the command decoder 93, and outputs the selected data to the selector 98.

The selector 96 selects one of the coefficient or the input data from the coefficient ROM and the data from the register circuit 95, and outputs a selected result to the multiplier 97. The selector 98 selects one of the coefficient or the input data from the coefficient ROM and the data from the register circuit 95, and outputs a selected result to the adder 99.

The multiplier 97 multiplies an output from the selector 96 by the data from the register circuit 95, and outputs a result thereof to the adder 99. The adder 99 adds an output from the selector 98 to an output from the multiplier 97, and outputs a result thereof to the register circuit 95. The register circuit 95 stores the output from the multiplier 97 in a register of the register circuit 95 corresponding to the write address from the command decoder 93.

The output register 88 stores data output from the processor 50, and outputs the data to an external device of the processor 50. For example, the output register 88 stores the frequency control data DFCQ which is output to the oscillation signal generation circuit 140 (or the dithering processor 160).

9. Aging Correction Using Karman Filter Process

In the present embodiment, an aging correction method using a Karman filter process is employed. Hereinafter, this method will be described.

FIG. 17 is a diagram illustrating results of measuring an oscillation frequency change due to aging. A transverse axis expresses the elapsed time (aging time), and a longitudinal axis expresses the frequency deviation (Δf/f₀) of an oscillation frequency. As indicated by C1 in FIG. 17, there are large variations caused by system noise or observation noise in measured values which are observed values. These variations also include a variation caused by the environmental temperature. In a situation in which there are large variations in the observed values, in the present embodiment, state estimation using a Karman filter process (for example, a linear Karman filter process) is performed in order to obtain an accurate true value.

Discrete time state equations of a time-series state space model are given by a state equation and an observation equation of the following (11) and (12).

x(k+1)=A·x(k)+v(k)  (11)

y(k)=x(k)+w(k)  (12)

Here, x(k) indicates a state at a time point k, and y(k) indicates an observed value (frequency control data). In addition, v(k) indicates system noise, w(k) indicates observation noise, and A is a system matrix. In a case where x(k) indicates an oscillation frequency (frequency control data), A corresponds to, for example, an aging rate (aging coefficient). The aging rate indicates a change rate of the oscillation frequency with respect to the elapsed time.

For example, it is assumed that a hold-over state occurs at a timing indicated by C2 in FIG. 17. In this case, aging correction is performed on the basis of a true value x(k) at the time point C2 at which the reference signal RFCK is stopped, and an aging rate (A) corresponding to an inclination indicated by C3 in FIG. 17. Specifically, as compensation (correction) for reducing a frequency change at the aging rate indicated by C3, for example, aging correction of sequentially changing the true value x(k) of the oscillation frequency (frequency control data) at the time point C2 with a correction value for canceling the frequency change is performed.

Details of the Karman filter process in the present embodiment will be described. In the Karman filter process of the present embodiment, the process is performed according to the following Equations (13) to (18), and thus a true value is estimated. In the present specification, the hat symbol “̂” indicating an estimated value is arranged with two letters as appropriate.

$\begin{matrix} {{{\hat{x}}^{-}(k)} = {{\hat{x}\left( {k - 1} \right)} + {D\left( {k - 1} \right)}}} & (13) \\ {{P^{-}(k)} = {{P\left( {k - 1} \right)} + {v(k)}}} & (14) \\ {{G(k)} = \frac{P^{-}(k)}{{P^{-}(k)} + {w(k)}}} & (15) \\ {{\hat{x}(k)} = {{{\hat{x}}^{-}(k)} + {{G(k)} \cdot \left( {{y(k)} - {{\hat{x}}^{-}(k)}} \right)}}} & (16) \\ {{P(k)} = {\left( {1 - {G(k)}} \right) \cdot {P^{-}(k)}}} & (17) \\ {{D(k)} = {{D\left( {k - 1} \right)} + {E \cdot \left( {{y(k)} - {{\hat{x}}^{-}(k)}} \right)}}} & (18) \end{matrix}$

{circumflex over (x)}(k): post-estimated value {circumflex over (x)}⁻(k): pre-estimated value P(k): post-covariance P⁻(k): pre-covariance G(k): Karman gain

In the Karman filter process, the Karman gain G(k) is obtained according to the above Equation (15) during observation update (observation process). The post-estimated value x^(̂)(k) is updated according to the above Equation (16) on the basis of the observed value y(k). The post-covariance P (k) of errors is updated according to the above Equation (17).

In time update (prediction process), as shown in the above Equation (13), the pre-estimated value x^(̂−)(k) at the next time step k is predicted by adding the post-estimated value x^(̂)(k−1) and the correction value D(k−1) at the time step k−1 together. As shown in the above Equation (14), the pre-covariance P⁻(k) at the next time step k is predicted on the basis of the post-covariance P(k−1) at the time step k−1 and the system noise v(k). As shown in the above Equation (18), the correction value D(k) at the next time step k is obtained by adding the correction value D(k−1) at the time step k−1 to a value obtained by multiplying an observation residual y(k)−x^(̂−)(k) by a constant E. In the present embodiment, as shown in the above Equation (13), the post-estimated value x^(̂)(k−1) is added to the correction value D(k−1) instead of multiplying the post-estimated value x^(̂)(k−1) by the system matrix A. In other words, the correction value D(k) corresponds to a predicted value for an aging rate.

FIG. 18 illustrates a detailed configuration example of the aging corrector 56.

The signal HOLDOVER is a signal whose logic level is “1” (active; hereinafter, simply referred to as “1”) in a hold-over period in which a hold-over state is detected. Specifically, a signal PLOCK which is a lock detection signal in the external PLL mode or a signal DTL which is a lock detection signal in the internal PLL mode is set as a signal PLLLOCK. In a case where the signal PLLLOCK has a logic level of “O” (inactive; hereinafter, simply referred to as “0”) and a signal SYNCCLK has “0”, the signal HOLDOVER has “1”, and, in a case where the signal PLLLOCK has “1” or the signal SYNCCLK has “1”, the signal HOLDOVER has “0”.

In a normal operation period, since the signal HOLDOVER has “0”, selectors 360 and 361 select terminal “0” sides. Consequently, in the normal operation period, the post-estimated value x^(̂)(k) and the correction value D(k) calculated by the Karman filter 54 are respectively held in registers 350 and 351.

If a hold-over state is detected, and the signal HOLDOVER has “1”, the selectors 360 and 361 select terminal “1” sides. Consequently, the selector 361 continuously outputs the correction value D(k) held in the register 351 at the hold-over detection timing during a hold-over period.

An adder 340 performs a process of sequentially adding the correction value D(k) (correction value) which is held in the register 351 and is output from the selector 361, to the post-estimated value x^(̂)(k) held in the register 350 at the hold-over detection timing, for each time step. Consequently, aging correction as expressed by the following Equation (19) is realized.

AC(k+1)=AC(k)+D(k)  (19)

10. Oscillation Circuit

FIG. 19 illustrates a configuration example of the oscillation circuit 150. The oscillation circuit 150 includes a current source IBX, a bipolar transistor TRX, a resistor RX, a variable capacitance capacitor CX1, and capacitors CX2 and CX3.

The current source IBX supplies a bias current to a collector of the bipolar transistor TRX. The resistor RX is provided between the collector and a base of the bipolar transistor TRX.

One end of the variable capacitance capacitor CX1 whose capacitance is variable is connected to one end of a resonator XTAL. Specifically, one end of the variable capacitance capacitor CX1 is connected to one end of the resonator XTAL via a first resonator terminal (resonator pad) of the circuit device 500. One end of the capacitor CX2 is connected to the other end of the resonator XTAL. Specifically, one end of the capacitor CX2 is connected to the other end of the resonator XTAL via a second resonator terminal (resonator pad) of the circuit device 500. One end of the capacitor CX3 is connected to one end of the resonator XTAL, and the other end thereof is connected to the collector of the bipolar transistor TRX.

A base-emitter current caused by oscillation of the resonator XTAL flows through the bipolar transistor TRX. If the base-emitter current increases, a current between the collector and the emitter of the bipolar transistor TRX increases, and thus a bias current which branches to the resistor RX from the current source IBX is reduced so that a collector voltage VCX is lowered. On the other hand, if a current between the base and the emitter of the bipolar transistor TRX is reduced, a collector-emitter current is reduced, and thus a bias current which branches to the resistor RX from the current source IBX increases so that the collector voltage VCX is heightened. The collector voltage VCX is fed back to the resonator XTAL via the capacitor CX3.

An oscillation frequency of the resonator XTAL has temperature characteristics, and the temperature characteristics are compensated by the output voltage VQ (frequency control voltage) from the D/A converter 80. In other words, the output voltage VQ is input to the variable capacitance capacitor CX1, and thus a capacitance value of the variable capacitance capacitor CX1 is controlled by the output voltage VQ. If the capacitance value of the variable capacitance capacitor CX1 changes, a resonance frequency of an oscillation loop changes, and thus a variation in an oscillation frequency due to the temperature characteristics of the resonator XTAL is compensated for. The variable capacitance capacitor CX1 is implemented by, for example, a variable capacitance diode (varactor).

11. Modification Examples

Next, various modification examples of the present embodiment will be described. FIG. 20 illustrates a configuration example of a circuit device according to a modification example of the present embodiment.

In FIG. 20, the D/A converter 80 is not provided in the oscillation signal generation circuit 140 unlike in FIG. 9. An oscillation frequency of the oscillation signal OSCK generated by the oscillation signal generation circuit 140 is directly controlled on the basis of the frequency control data DFCQ from the processor 50. In other words, an oscillation frequency of the oscillation signal OSCK is controlled without using the D/A converter.

For example, in FIG. 20, the oscillation signal generation circuit 140 has a variable capacitance circuit 142 and an oscillation circuit 150. The variable capacitance circuit 142 is provided instead of the variable capacitance capacitor CX1 illustrated in FIG. 19, and one end of the variable capacitance circuit 142 is connected to one end of the resonator XTAL.

A capacitance value of the variable capacitance circuit 142 is controlled on the basis of the frequency control data DFCQ from the processor 50. For example, the variable capacitance circuit 142 is provided with a plurality of capacitors (capacitor array), and a plurality of switch elements (switch array) each of which allows turning-on and turning-off to be controlled on the basis of the frequency control data DFCQ. Each of the plurality of switch elements is electrically connected to each of the plurality of capacitors. The plurality of switch elements are turned on or off, and thus the number of capacitors whose one ends are connected to one end of the resonator XTAL among the plurality of capacitors changes. Consequently, a capacitance value of the variable capacitance circuit 142 is controlled, and thus a capacitance value of the resonator XTAL changes. Therefore, a capacitance value of the variable capacitance circuit 142 can be directly controlled by the frequency control data DFCQ, and thus an oscillation frequency of the oscillation signal OSCK can be controlled.

In a case where a PLL circuit is formed by using the circuit device of the present embodiment, the PLL circuit may be formed according to a direct digital synthesizer method. FIG. 21 illustrates a circuit configuration example in a case of the direct digital synthesizer method.

A phase comparator 380 (comparison calculator) performs comparison calculation between the reference signal RFCK and the oscillation signal OSCK (an input signal based on the oscillation signal). A digital filter 382 performs a smoothing process on phase errors. A configuration and an operation of the phase comparator 380 are the same as those of the internal phase comparator 40 illustrated in FIG. 1, and may include the counter 42 or the like. The digital filter 382 corresponds to the phase error converter 51, the loop filter 55, and the frequency control data converter 57 illustrated in FIG. 4. A numerical controlled oscillator 384 is a circuit which digitally synthesizes any frequency or waveform by using a reference oscillation signal from a reference oscillator 386 having the resonator XTAL. In other words, instead of controlling an oscillation frequency on the basis of a control voltage from a D/A converter, such as a VCO, the oscillation signal OSCK having any oscillation frequency is generated through a digital calculation process by using digital frequency control data and the reference oscillator 386 (resonator XTAL).

12. Oscillator, Electronic Apparatus, and Vehicle

FIG. 22 illustrates a configuration example of an oscillator 400 provided with the circuit device 500 of the present embodiment. As illustrated in FIG. 22, the oscillator 400 includes a resonator 420 and the circuit device 500. The resonator 420 and the circuit device 500 are mounted in a package 410 of the oscillator 400. A terminal of the resonator 420 is electrically connected to a terminal (pad) of the circuit device 500 (integrated circuit device; IC) via an internal wiring of the package 410.

FIG. 23 illustrates a configuration example of an electronic apparatus 700 including the circuit device 500 of the present embodiment. The electronic apparatus 700 includes the circuit device 500 of the present embodiment, the resonator 420 such as a quartz crystal resonator, an antenna ANT, a communication device 510, a processor 520, and the like. The electronic apparatus 700 may include an operation device 530, a display 540, and a storage 550. The oscillator 400 is formed of the resonator 420 and the circuit device 500. A configuration of the electronic apparatus is not limited to the configuration illustrated in FIG. 23, and may be variously modified by omitting some constituent elements or adding other constituent elements thereto.

As the electronic apparatus 700 illustrated in FIG. 23, there may be various apparatuses, for example, a network related apparatus such as a base station or a router, a highly accurate measurement apparatus, a GPS built-in clock, a wearable apparatus such as a biological information measurement apparatus (a sphygmograph, a pedometer, or the like) or a head mounted display, a portable information terminal (mobile terminal) such as a smart phone, a mobile phone, a portable game apparatus, a notebook PC, or a tablet PC, a content providing terminal which delivers content, and a video apparatus such as a digital camera or a video camera.

The communication device 510 (wireless circuit) performs a process of receiving data from an external apparatus or transmitting data to the external apparatus, via the antenna ANT. The processor 520 performs a process of controlling the electronic apparatus 700, or various digital processes on data which is transmitted and received via the communication device 510. The function of the processor 520 may be realized by, for example, a processor such as a microcomputer.

The operation device 530 is used for a user to perform an input operation, and may be implemented by, for example, an operation button or a touch panel display. The display 540 displays various pieces of information, and may be implemented by, for example, a liquid crystal display or an organic EL display. In a case where a touch panel display is used as the operation device 530, the touch panel display also functions as the operation device 530 and the display 540. The storage 550 stores data, and a function thereof may be realized by a semiconductor memory such as a RAM or a ROM, or a hard disk drive (HDD).

FIG. 24 illustrates an example of a vehicle including the circuit device 500 of the present embodiment. The circuit device 500 (the oscillator 400 including the circuit device 500) of the present embodiment may be incorporated into, for example, various vehicles such as a car, an aircraft, a motorbike, a bicycle, and a ship. The vehicles are pieces of equipment or instruments which are provided with, for example, driving mechanisms such as engines or motors, steering mechanisms such as handles or rudders, and various electronic apparatuses (on-vehicle apparatuses), and move on the ground, in the air, and in the sea. FIG. 24 schematically illustrates an automobile 206 as a specific example of the vehicle. The oscillator (not illustrated) including the circuit device and the resonator of the present embodiment is incorporated into the automobile 206. A control device 208 operates on the basis of a clock signal generated by the oscillator. The control device 208 controls hardness and softness of a suspension or a brake of each car wheel 209, for example, in accordance with the attitude of a car body 207. For example, automatic driving of the automobile 206 may be realized by the control device 208. An apparatus into which the circuit device or the oscillator of the present embodiment is incorporated is not limited to the control device 208, and the circuit device or the oscillator of the present embodiment may be incorporated into various apparatuses (on-vehicle apparatuses) provided in a vehicle such as the automobile 206.

FIG. 25 illustrates a configuration example of a base station 800 (base station apparatus) which is one of the electronic apparatuses. Aphysical layer circuit 600 performs a process on a physical layer in a communication process using a network. A network processor 602 performs a process on a higher-order layer (a link layer or the like) than the physical layer. A switch 604 performs various switching processes in the communication process. A DSP 606 performs various digital signal processes which are necessary in the communication process. An RF circuit 608 includes a reception circuit formed of a low noise amplifier (LNA), a transmission circuit formed of a power amplifier, a D/A converter, an A/D converter, and the like.

A selector 612 outputs either a reference signal RFCK1 from a GPS 610 or a reference signal RFCK2 (a clock signal from the network) from the physical layer circuit 600, to the circuit device 500 of the present embodiment as the reference signal RFCK. The circuit device 500 performs a process of synchronizing an oscillation signal (an input signal based on the oscillation signal) with the reference signal RFCK. Various clock signals CK1, CK2, CK3, CK4 and CK5 having different frequencies are generated, and are supplied to the physical layer circuit 600, the network processor 602, the switch 604, and the DSP 606, and the RF circuit 608.

According to the circuit device 500 of the present embodiment, in a base station as illustrated in FIG. 25, an oscillation signal can be synchronized with the reference signal RFCK, and the clock signals CK1 to CK5 having the high frequency stability, generated on the basis of the oscillation signal, can be supplied to the respective circuits of the base station.

Although the present embodiment has been described as above in detail, it can be easily understood by a person skilled in the art that various modifications without substantially departing from the new matters and effects of the invention are possible. Therefore, these modifications are all included in the scope of the invention. For example, in the specification or the drawings, the terminologies which are mentioned at least once along with different terminologies which have broader meanings or the same meanings may be replaced with the different terminologies in any location of the specification or the drawings. All combinations of the present embodiment and the modification examples are included in the scope of the invention. In addition, configurations, operations, and the like of the phase comparator, the processor, the oscillation signal generation circuit, the circuit device, the oscillator, the electronic apparatus, and the vehicle are also not limited to the above description of the present embodiment, and may have various modifications. 

What is claimed is:
 1. A circuit device comprising: a phase comparator that compares a phase of an input signal and a phase of a reference signal to generate phase comparison result data, the input signal being based on an oscillation signal; a processor that performs a digital signal process on the phase comparison result data to generate frequency control data, and when a hold-over state occurs due to absence or abnormality of the reference signal and subsequently ends, the processor performing the digital signal process by using hold-over end use data, which is data in use when the hold-over state ends; and an oscillation signal generation circuit that generates the oscillation signal, which has an oscillation frequency set based on the frequency control data.
 2. The circuit device according to claim 1, wherein the hold-over end use data is calculation result data in the digital signal process, held when the hold-over state occurs, or data obtained through a correction process in a hold-over period.
 3. The circuit device according to claim 2, wherein the hold-over end use data is the calculation result data, and the processor temporarily stops the digital signal process when the hold-over state occurs, and performs the digital signal process by using the calculation result data when the hold-over state ends.
 4. The circuit device according to claim 2, wherein the hold-over end use data is the data obtained through the correction process, and the correction process is at least one of an aging correction process and a temperature compensation process.
 5. The circuit device according to claim 2, wherein the digital signal process includes a digital filter process including a proportion process on the phase comparison result data and an integration process on the phase comparison result data, and when the hold-over state occurs, result data in the integration process is held as the hold-over end use data.
 6. The circuit device according to claim 1, wherein the processor stops the digital signal process when the hold-over state occurs, and resumes the digital signal process when the hold-over state ends.
 7. The circuit device according to claim 1, wherein the processor performs the digital signal process including at least one of a temperature compensation process and an aging correction process on the frequency control data, and a process of correcting capacitance characteristics of a variable capacitance capacitor connected to a resonator for generating the oscillation signal, and a digital filter process on the phase comparison result data.
 8. The circuit device according to claim 1, wherein the processor: performs a process of estimating a true value for an observed value of the frequency control data based on the phase comparison result data through a Karman filter process in a period before the hold-over state is detected, and holds the true value at a time corresponding to when the hold-over state is detected, and performs a calculation process based on the true value so as to generate the frequency control data having undergone aging correction.
 9. An oscillator comprising: the circuit device according to claim 1; and a resonator that is used to generate the oscillation signal.
 10. An oscillator comprising: the circuit device according to claim 2; and a resonator that is used to generate the oscillation signal.
 11. An oscillator comprising: the circuit device according to claim 3; and a resonator that is used to generate the oscillation signal.
 12. An oscillator comprising: the circuit device according to claim 4; and a resonator that is used to generate the oscillation signal.
 13. An oscillator comprising: the circuit device according to claim 5; and a resonator that is used to generate the oscillation signal.
 14. An electronic apparatus comprising the circuit device according to claim
 1. 15. A vehicle comprising the circuit device according to claim
 1. 16. A circuit device comprising: a phase comparator that compares a phase of an input signal and a phase of a reference signal to generate phase comparison result data, the input signal being based on an oscillation signal, a hold-over state occurring when the reference signal is absent or abnormal; a processor that performs a digital signal process on the phase comparison result data to generate frequency control data, the processor performing the digital signal process using: initial data at a time when the circuit device initially starts; and hold-over end use data at a time when the hold-over state ends, the hold-over end use data being data in use at the time when the hold-over state ends; and an oscillation signal generation circuit that generates the oscillation signal, which has an oscillation frequency set based on the frequency control data. 